#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(15);
    ll a, b, c;
    cin >> a >> b >> c;
    cout << ((a + c) == 2 * b ? "Yes" : "No") << '\n';
}